But Pinterest, the most talked-about startup of the spring, went after a different crowd when it introduced its service in 2009. The site lets users create “virtual pinboards” where they can collect images from around the Web and share them with friends and strangers.

“We showed it to folks from all walks of life, lifestyle bloggers, crafters and hobbyists,” said Ben Silbermann, a founder and the chief executive of

Pinterest.com. “The early people were from the area where I grew up, in Des Moines, and the site grew very organically from there.”

And grow it has. Palo Alto-based Pinterest — which has 20 employees and 12 million-and-counting users — declined to provide specific figures, but data from analytics firms indicate the company’s traffic has been rising exponentially. Nielsen reported that Pinterest had 16.1 million unique visitors in January in the United States alone, double the number it had in November.

That is the kind of gain that most entrepreneurs can only dream of.

“It defies the mold that you have to build something for New York and San Francisco and then spread it out from there,” said Chris Dixon, an investor in Skype, Skillshare, GroupMe and other companies and the chief executive of Hunch, which was acquired by eBay this year.

Investors include prominent venture capital firm Andreessen Horowitz and Jeremy Stoppelman, the CEO of reviews site Yelp, who provided some of Pinterest’s $40 million in financing. Pinterest is privately held and does not disclose how much money it is making. The site doesn’t have advertisements or a clear path to profitability, but that’s common with Internet companies just starting out.

Pinterest’s low-key approach makes sense for the site because it aims to appeal to people interested in creating curated collections of photographs around a topic, like midcentury modern furniture, fancy cakes or fashion trends like floral fabrics. Essentially they use the site’s “Pin It” tool to make scrapbooks that link back to the original source of each photo, whether it be a museum site, a fashion blog or an online store.

Susan Etlinger, an analyst at the Altimeter Group who advises companies on how to use technology, said Pinterest was tapping in to behavior that went beyond simply sharing. Etlinger said it was akin to early forums on the Web where users would congregate around a very specific topic — vegan recipes or tattoo art, for example — because it let them drill down into things that truly interested them, and explore what others had shared on a subject.

Analysts say Pinterest’s popularity has caused such a shake-up around the Web because there is a large overlap between the people who gravitate toward the site — comScore estimates that 68 percent are women — and those who visit mass merchandise and e-commerce sites.

“The Pinterest audience is the same audience that shops online, which is very unique,” said Radha Subramanyam, senior vice president for media analytics at Nielsen. Pinterest, she said, “could very quickly translate these interests into transaction opportunities.”

Access to Pinterest is currently by invitation only, so those looking to join need to request one from the company or ask a friend already on it.

Pinterest, like game maker Zynga and many others before it, likely wouldn’t have grown as popular without the help of Facebook, the world’s largest online social network. Facebook said last month that the number of its users visiting Pinterest every day grew by 60 percent after it was integrated into the site in January.

Because it’s rooted in unencumbered image-sharing, Pinterest has also raised copyright concerns. Lawyers, however, say its legal standing is no different from those of other popular websites, such as YouTube or Facebook.

And the network recently caught heat for not disclosing that it attached so-called affiliate links into product images posted there, allowing it to collect payments from purchases made by users who clicked on the pictures. The company subsequently stated that the affiliate links were a test, not an essential part of its business model.

The Associated Press, San Jose Mercury News and The Boston Globe contributed to this report.